Enhanced removal of NO-N from water using Fe-Al modified biochar: behavior and mechanism.

To remove NO-N from water, coconut shell biochar (CSB) was modified by a solution of FeCl, a solution of AlCl and a mixture solution of FeCl and AlCl respectively. The obtained modified biochar with the best effect of NO-N adsorption was screened out to explore the adsorption behavior and mechanism of NO-N removal by batch experiments and kinetics and thermodynamics and correlated characterization. The results indicated that the mixture solution of FeCl- and AlCl- modified CSB (Fe-Al/CSB) showed the best adsorption performance for NO-N removal. Iron and aluminum elements existed on the surface of Fe-Al/CSB in the form of FeOOH, FeO, Fe, and AlO respectively. The adsorption process could reach equilibrium in 20 min. An acidic condition was favorable for NO-N adsorption. The presence of coexisting anions was not conducive for NO-N adsorption. The quasi-second-order model and Freundlich model could be well fitted in the adsorption process. The maximum adsorption capacity of Fe-Al/CSB fitted by the Langmuir model could reach 34.20 mg/g. The adsorption of NO-N by Fe-Al/CSB was an endothermic and spontaneous process. Ligand exchange and chemical redox reaction were the NO-N adsorption mechanisms which led to NO-N adsorption by Fe-Al/CSB.